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The title, more or less, sums it up. I plan to bury some THHN/THWN-2 feeders, and my jurisdiction allows a 6" bury depth if I use IMC or RMC. I plan to use IMC, which comes with both a male and female threaded end. Do I need to use any sealant on these threads to prevent water ingress?

Unfortunately, I don't think I will be lucky enough to avoid cutting any conduit to get the length I need. How do I couple unthreaded IMC underground? Do I need to use liquid-tight fittings?

My guess is that I don't need any sealants or special fittings because the THWN-2 wires are suitable for wet locations, but I'd like to make sure, in case I need to order special fittings.

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  • Renting a pipe threading machine is the best way. There’s also threaded F/F couplings available. – Tyson May 22 '18 at 19:48
  • Assume all outdoor conduit is full of water all the time. The defense is in the quality of wire. – Harper May 22 '18 at 20:56
  • @Tyson Are you suggesting to only make threaded connections? If it uses "iron pipe" threads, then I can just get the local store to thread it for me. – Hari Ganti May 22 '18 at 23:27
  • @Harper Don't worry, I've seen you post that enough to get the picture. The wires are unbroken, so I don't expect that to be an issue. I'm just interested in how to join the conduit segments properly. – Hari Ganti May 22 '18 at 23:29
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Do I need to use any sealant on these threads to prevent water ingress?

No you should not use any sealants, chemicals or compounds that are not specifically approved for electrical installations.

How do I couple unthreaded IMC underground? Do I need to use liquid-tight fittings?

The best way to couple unthreaded IMC is with threadless IMC compression couplings. Yes they do make them and they are expensive and they are not a stock item. Exercise caution when using them. They have a tendency to pull apart during expansion and contraction of the soil. Try and use them where there is less of a chance to do this, meaning at the beginning and end of the trench around the 90 degree ell coming out of the ground or use with an expansion coupling.

Good luck.

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  • Thanks. I appreciate the remark about using compression fittings. I should only need them at one end, just before a transition to an elbow, which seems like a good use case. – Hari Ganti May 23 '18 at 17:52

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